Old explosives

[paul.mercer]

Gentlemen,
In a recent newspaper article the subject of the sunken liberty ship in the Thames estury was revisited. Appraerntly it has approx 3000 tons of explosives (out of the original 6000) still on board and has been a continual thorn in the side of the Ministry of Defence ever since WW2. Also, I believe that Truk Lagoon has a number of ships filled with shells, mines etc. My question is this, just how dangerous are these munitions? After all, items like shells, cordite etc are not designed to be underwater like sea mines so after almost 70 years underwater would not the explosive be so wet that detonation is unlikely?
I was told that one of the big underground mines dug by the British in WW1 went off in about 1955 and that there is at least another one which has never been found, so after almost 100 years would it now be dormant?

[tommy303]

To a large degree it depends on the type of explosive used in the munitions. TNT itself is quite stable and non-hydroscopic. It does not deteriorate in the presence of water alone and provided one intentionally gives it a suitable stimulus with another explosive, it can be made to detonate even after decades of being submerged. The same might not be the case with gaines containing picric acid, as many did even into WW2 or shells containing Explosive D (Ammonium Picrate). The presence of bromide salts in brackish estuary water and sea water tends to form unstable compounds when in contact with those explosives. This can make them somewhat dangerous to handle or move after long exposure, and if the bombs or shells have their gaines in place, they might be highly dangerous.

In most cases, if the casing of the bomb or shell rusts away, the explosive will eventually be eroded away as well by the action of water currents and the abrasive action of sand, but until such a time, any mass of explosive will still be able to detonate.

[paul.mercer]

Thanks Tommy,
Divers found a German parachute mine off Falmouth a couple of weeks ago, from the film it looked just like a old elongated dustbin covered in weed, but when the Naval Bomb Disposal team put a charge against it there was two bangs as it went up a fairly small one for the charge and one very big one for the mine itself- over 65 years later!